[PATCH v2 0/6] alloc_tag: introduce IOCTL-based filtering for MAP

[Abhishek Bapat <abhishekbapat@google.com>]

Currently, memory allocation profiling data is primarily exposed through
/proc/allocinfo. While useful for manual inspection, this text-based
interface poses challenges for production monitoring and large-scale
analysis:

1. Userspace must parse large amounts of text to extract specific
fields.
2. To find specific tags, userspace must read the entire dataset,
requiring many context switches and high data copying.
3. The kernel currently aggregates per-CPU counters for every allocation
size, even those the user intends to filter out immediately.

This series introduces a new IOCTL-based binary interface for allocinfo
that supports kernel-side filtering. By allowing the user to specify a
filter mask, we significantly reduce the work performed in-kernel and
the amount of data transferred to userspace.

Performance measurements were conducted on an Intel Xeon Platinum 8481C
(224 CPUs) with caches dropped before each run.

The IOCTL mechanism shows a ~20x performance improvement for
filtered queries. The kernel avoids the expensive per-CPU counter
aggregation (alloc_tag_read) for any tags that fail the initial string
or location filters.

Scenario 1: Specific File Filtering (arch/x86/events/rapl.c)
1. Traditional (cat /proc/allocinfo | grep): 22ms (sys)
2. IOCTL Interface: 1ms (sys)

Scenario 2: Compound Filtering (Filename + Size)
1. Traditional: (cat ... | grep | awk): 21ms (sys)
2. IOCTL Interface: 1ms (sys)

Scenario 3: Size-Based Filtering (min_size = 1MB)
1. Traditional: (cat ... | awk): 21ms (sys)
2. IOCTL Interface: 14ms (sys)

v2 changes:
- Patch 1/6: Introduced locking for m->private. Also included the new uapi
header file in MAINTAINERS list.
- Patch 2/6: Handled the case where ALLOCINFO_FILTER_MASK_MODNAME is
passed but ct->modname is NULL.
- Patch 3/6: Moved min_size and max_size outside of struct allocinfo_tag
into struct allocinfo_filter. Added validation that min_size <=
max_size. Prefetched alloc_tag_counters if size based filter masks are
provided to avoid assimilating per-cpu counters twice.
- Patch 5/6: Removed the hardcoded logic to skip the header, instead the
test will skip lines that don't match the format. Also included the
newly added alloc_tag selftests directory in MAINTAINERS list.

Abhishek Bapat (5):
  alloc_tag: add ioctl filters to /proc/allocinfo
  alloc_tag: add size-based filtering to ioctl
  alloc_tag: add accuracy based filtering to ioctl
  kselftest: alloc_tag: add kselftest for ioctl interface
  kselftest: alloc_tag: extend the allocinfo ioctl kselftest

Suren Baghdasaryan (1):
  alloc_tag: add ioctl to /proc/allocinfo

 .../userspace-api/ioctl/ioctl-number.rst      |   2 +
 MAINTAINERS                                   |   2 +
 include/linux/codetag.h                       |   1 +
 include/uapi/linux/alloc_tag.h                |  87 +++
 lib/alloc_tag.c                               | 303 ++++++++++-
 lib/codetag.c                                 |  11 +
 tools/testing/selftests/alloc_tag/Makefile    |   9 +
 .../alloc_tag/allocinfo_ioctl_test.c          | 505 ++++++++++++++++++
 8 files changed, 918 insertions(+), 2 deletions(-)
 create mode 100644 include/uapi/linux/alloc_tag.h
 create mode 100644 tools/testing/selftests/alloc_tag/Makefile
 create mode 100644 tools/testing/selftests/alloc_tag/allocinfo_ioctl_test.c

-- 
2.54.0.746.g67dd491aae-goog